For example, Patent Literature 1 discloses an electrothermal heater including: abase material having a sheet form; a heater wire arranged on a surface of the base material; a heat insulating material such as glass fiber felt or silica felt; and a cover member for housing these components, in which at least part of the cover member contains fluororesin fiber fabric or aromatic nylon fiber fabric.
In addition, for example, Patent Literature 2 discloses a mantle heater having a heating element and a non-flammable and flame-retardant fiber sheet material having a heat insulating property interposed between an inner layer material and an outer layer material each having flexibility and being formed of a synthetic resin sheet.
In addition, Patent Literature 3 discloses a pipe heating heater including a cylindrical sheet heating element in a halved form and a clip for opening and closing the sheet heating element.